1. Purpose of the Invention
This invention relates to certain new and useful improvements in impulse generators and method of use therefor, and, more particularly, to impulse generators in connection with phosphor excitable lamps for intermittently energizing the lamp.
2. Brief Description of the Prior Art
For many years, phosphor excitable lamps have been used, including the well-known fluorescent lamp, and which have replaced the conventional incandescent lamp in many applications. These phosphor excitable lamps generally operate on the principle of generating ultraviolet radiation and converting the ultraviolet radiation to visible light by energizing the phosphor coating and hence exciting the phosphors generated by the phosphor coating. Phosphor excitable lamps include, for example, the gaseous discharge lamp and the electroluminescent lamp.
The gaseous discharge lamp, which includes the so-called fluorescent lamp, operates on a principle which makes use of ultraviolet energy generated by a mercury vapor in an inert gas and which activates a coating of a fluorescent material, often referred to as a phosphor, on the inner surface of the glass tube. The phosphor acts as a transformer converting the ultraviolet radiation into visible light.
In most conventional fluorescent lamps and similar gas discharge lamps, the lamp includes a hot cathode located on the interior thereof and connected to terminals on the exterior of the lamp. In the electroluminescent lamp, a capacitive effect is achieved with a phosphor coating on a transparent sheet and with a second electrode being comprised of an aluminum or similar metal sheet. These lamps are operable in conjunction with a number of conventionally known ballasts. The ballast generally is a series reactor transformer and includes a large number of windings. Thus, the ballast acts as an inductive device to increase the voltage for igniting the phosphor excitable lamp. The ballast primarily serves to both ignite the lamp and to also limit the current to the lamp. Immediately after the lamp is ignited, the impedance of the lamp drops to an almost zero level and, hence, it is necessary to limit the current after ignition in order to avoid burning-up the lamp. The inductive reactance in the conventional ballast operates to limit the current after ignition of the lamp.
There are many disadvantages of the conventional ballast system used in connection with phosphor lamps. One of the disadvantages lies in the weight and size factor of the conventional ballast. Due to the heavy transformer, provision must be made in each conventional lamp fixture in order to mount and support the weight of the ballast. Moreover, if they are used for any excessive period of time, the ballast may heat up and may tend to burn out and require replacement thereof.
In addition to the above, the transformer core in the ballast will tend to vibrate and generate a hum in the audible frequency spectrum. While this hum may not have a great amplitude, it is, nevertheless, distracting and uncomfortable to an individual in proximity to the light source. In addition to the above problems, the vibration of the core in the ballast would often tend to create a flicker in the light. While the flicker may occur at a high frequency, it is nevertheless oftentimes visible and apparent to the observer.
Another disadvantage of the conventional ballast is that large capacitors are oftentimes required to correct the power factor and phase displacement. These capacitors are relatively expensive due to their size and thus substantially increase the overall cost of the ballast. Even moreso, the use of an inductive device of this type often generates a significant amount of heat and, in many cases, where the lamp is not mounted in an environment where air flow can dissipate the heat, other means must be employed to dissipate the heat generated by the ballast. The conventional ballast also tends to generate undesirable radio frequency signals which may interfere with RF operated equipment.
One of the primary disadvantages of the conventional ballasts, at least in present energy shortage times, is that the ballast requires a very substantial amount of current in order to maintain energiziation of the lamp. After the lamp has been ignited, a continuing current source is applied to the two electrodes of the lamp in order to maintain energization thereof. However, it has been found in the present invention that it is possible to maintain energization of the lamp even for a short interval, even after cessation of current supply.